Gas flotation tank

ABSTRACT

A gas flotation tank is provided that includes a series of adjacent chambers which impart a rotational current therein. Each chamber is separated from a skim oil trough by a skimming weir. Each chamber comprises an alternating fluid communication device between adjacent chambers allowing fluid communication between adjacent chambers in the form of a communication port in the dividing wall between adjacent chambers and a chamber outlet in conjunction with a perforated plate and the outlet is positioned in fluid communication with the final chamber. An optional coalescing media may be positioned in or proximate the communication port to absorb or coalesce contaminants as they pass therethrough.

RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 14/914,610 filed Feb. 25, 2016, which is the U.S.National Phase of PCT/CA/2014/050751 filed Aug. 8, 2014, which in turnclaims priority to U.S. Ser. No. 13/975,750 filed Aug. 26, 2013. Thesubject matter of each of these applications is incorporated herein byreference in entirety.

FIELD OF THE INVENTION

The invention relates to gas flotation tanks for separating hydrocarbonsfrom produced water and more specifically to gas flotation tanks withreduced structural and internal piping that prevent, reduce or at leastmitigate short circuiting.

BACKGROUND

Gas flotation tanks are used to separate unwanted phases or contaminantssuch as hydrocarbons from produced water generally by allowing orfacilitating the rising of the unwanted phases or contaminants to thesurface of produced water. The hydrocarbons may then be removed viaskimming of the surface of the produced water.

One typical gas flotation tank comprises of a number of chambersseparated by a dividing wall but in fluid communication with each other.During operation, produced water is input into the tank and a rotationalcurrent is generated promoting hydrocarbon to rise to the surface of thewater in the tank while forcing cleaner more purified water towards thebottom of the tank. By passing the lower water to an adjacent chambervia a fluid communication port, each successive chamber containsproduced water having a lower content of hydrocarbons until a desiredpurity level is reached and the water is output from the gas flotationtank. One problem with such a design is the need for heavily reinforceddivider walls between each chamber of the gas flotation tank as fluidlevels in each chamber can be unequal and the difference in fluid levelcan be significant enough to damage the divider wall and the tank. Inaddition, depending on the location of the fluid communication portbetween each divider wall of the tank, water can short circuit acrossthe chambers resulting in water in the final chamber being output with ahigher than desirable hydrocarbon content.

To avoid short circuiting, one gas flotation tank includes aninterconnecting pipe to connect the chambers in series without creatinga short circuit from the inlet to the outlet. The interconnecting pipeis located in such a way that the water considered to be cleanest istaken from one chamber to the next, released near the surface, anddispersed in a fashion (in conjunction with a water weir) to create aflow pattern and velocities that facilitate skimming of the surfacehydrocarbon towards an oil skimming trough. The interconnecting pipealso acts as a region in which “micro-bubbles” may be introduced beforeentering subsequent chambers to ensure even mixing with flow going intoeach chamber.

However, the interconnecting pipe allows for, in an upset condition, anuncontrolled increase or decrease inlet flow, resulting in a large leveldifference between chambers that can collapse the internal walls hencerequiring a need to heavily reinforce the tank. In order to minimize therisk of large level differences the interconnecting pipe size can beincreased. However, such an increase can obstruct the flow patternwithin the tank as well as reduce the working volume of the chamber thusrendering the tank less efficient. In addition, such an interconnectingpipe is limited by standard pipe and rolled plate sizes and associatedcosts. Furthermore, filling and draining the tank is a delicate processthat requires careful monitoring of the level in each chamber.

Another type of flotation tank is referred to as a serpentine tank andincludes a number of chambers, each chamber separated by a partitionwherein a portion of the partition is a perforated plate or opening,allowing for the balancing of the chambers. However, a serpentine tankallows only for horizontal flow through the tank, wherein gravity andtime are used for the separation of the unwanted phases. The fluid in aserpentine tank flows substantially in one direction inside the chamber(lengthwise) and exits the chamber through the perforated plate, or opensection, to the adjacent chamber where it flows horizontally the lengthof that chamber, repeating for as many chambers as is provided in agiven tank, hence the term “serpentine”. This pattern of going end toend also creates the requirement for individual skimming points in eachchamber, which also requires additional nozzles on the tank, externalpiping, and valves for removing the unwanted phases.

A need therefore exists for a gas flotation tank that prevents, reducesor mitigates short circuiting while reducing or removing the dependencyon interconnecting piping.

SUMMARY

A gas flotation tank for separating contaminants from fluid is provided.The tank includes a series of adjacent chambers which impart arotational current therein through the use of a sloped weir in eachchamber. Each chamber is separated from a skim oil trough by a skimmingweir over which the contaminants pass. Each adjacent chamber is fluidlyconnected via an interconnecting passage that allows for the transfer ofreduced contaminant fluid to an adjacent chamber for further contaminantreduction. An alternating setup of fluid passages and connector portsbetween adjacent chambers allows for at least partial equalization ofthe fluid level between adjacent chambers and further mitigates, reducesor prevents short circuiting of the fluid as it passes from chamber tochamber. An optional coalescing media may be positioned in or proximateone or more of the interconnecting passages to absorb or coalescecontaminants as they pass therethrough.

In one embodiment, there is provided a flotation tank for removing acontaminant from fluid input into the flotation tank, the flotation tankcomprising;

-   -   a floor defining a bottom of the tank and a depending wall        defining the sides of the tank;    -   a series of adjacent chambers within the tank separated from        each other by dividing walls, each chamber comprising a sloped        weir for inducing a rotational current within the chamber;    -   a skim oil trough spanning each chamber and separated from each        chamber by a skimming weir, the skimming weir opposite the        sloped weir;    -   an inlet in fluid communication with a chamber of the series of        adjacent chambers for inputting a fluid comprising a        contaminant, the inlet situated proximate the sloped weir of the        series of adjacent chambers for inducing a rotational current to        fluid input into the chamber;    -   each chamber in fluid communication with the adjacent chambers        via an interconnecting passage positioned substantially towards        the bottom of the dividing wall of each chamber and        substantially opposite the skim oil trough, the interconnecting        passage allowing passage of fluid from a chamber to a backside        of the sloped weir of the adjacent chamber;    -   a connector port in the dividing wall between two adjacent        chambers for providing fluid communication between the two        adjacent chambers;    -   a fluid passage in the sloped weir of at least one of the        chambers of the series of adjacent chambers allowing for fluid        transfer between adjacent chambers through the sloped weir of        the at least one chamber; and    -   an outlet in fluid communication with one of the chambers of the        series of adjacent chambers outputting produced water;    -   a coalescing media positioned in or proximate one or more of the        interconnecting passages for absorbing or coalescing        contaminants as they pass through the interconnecting passage;    -   wherein the connector port and the fluid passage are situated in        alternating adjacent chambers.

In a further embodiment of a flotation tank to that described above, theconnector port is positioned in the base of the dividing wall proximatethe skimming weir.

In a further embodiment of a flotation tank to that described above, theinterconnecting passage is positioned at one end proximate the base ofthe sloped weir and at the other end in proximity to a backside of thesloped weir of the adjacent chamber.

In a further embodiment of a flotation tank to that described above, thefluid passage is positioned proximate the base of the sloped weir.

In a further embodiment of a flotation tank to that described above, thefluid passage is a perforated plate in the sloped weir.

In a further embodiment of a flotation tank to that described above, theoutlet is positioned proximate the base of the wall of the finalchamber.

In a further embodiment of a flotation tank to that described above, theinlet is positioned in the first chamber.

In a further embodiment of a flotation tank to that described above,each set of adjacent chambers comprises either a connector port or afluid passage in alternating format allowing for equalization of thefluid level in adjacent chambers while preventing short circuiting ofthe fluid through the tank to the final chamber.

In a further embodiment of a flotation tank to that described above, thetank further comprises a manifold in fluid communication with eachchamber for inputting or withdrawing fluid from the tank.

In a further embodiment of a flotation tank to that described above, thesloped weirs of the tank are aligned with one another in the adjacentchambers.

In a further embodiment of a flotation tank to that described above, thesloped weirs of the tank are offset with one another in at least two ofthe adjacent chambers.

In a further embodiment of a flotation tank to that described above, anupper edge of the skimming weir comprises at least one notch to promotetransfer of the unwanted phase into the skim oil trough.

In a further embodiment of a flotation tank to that described above, thetank further comprises an inlet in fluid communication with each chamberfor injecting a gas into the chamber, optionally in the form ofmicro-bubbles.

In a further embodiment of a flotation tank to that described above, thecontaminant comprises hydrocarbon, emulsified oils, or heavy oils.

In a further embodiment of a flotation tank to that described above, thefluid is produced water.

In a further embodiment of a flotation tank to that described above, thecoalescing media is a fixed media.

In a further embodiment of a flotation tank to that described above, thecoalescing media is a non-fixed media.

In a further embodiment of a flotation tank to that described above, thecoalescing media is positioned in the interconnecting passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of one illustrative embodiment of a gasflotation tank including five chambers;

FIG. 2 is a top plan view of the gas flotation tank shown in FIG. 1;

FIG. 3 is an isometric side view of the gas flotation tank shown in FIG.1;

FIG. 4 is a cross sectional view of the gas flotation tank shown in FIG.1 along the dividing wall between the first and second chamber;

FIG. 5 is a cross sectional view of the gas flotation tank shown in FIG.1 along the third chamber showing the perforated plate allowing foringress of fluid from second chamber into the third chamber;

FIG. 6 is a cross sectional view of the gas flotation tank shown in FIG.1 between the sloped weir and the skim oil trough showing the connectingports between the first and second chamber and the third and fourthchamber allowing for fluid communication between these chambers andingress of fluid from the first chamber into the second chamber and fromthe third chamber into the fourth chamber;

FIG. 7 is a chart of chamber residence time against cumulative removalefficiency demonstrating increased removal efficiency as the number ofsequential chambers increases;

FIG. 8 is an isometric view of a further illustrative embodiment of agas flotation tank including five chambers wherein the sloped weirs ofthe chambers are arranged at varying positions;

FIG. 9 is an isometric cross sectional view of the gas flotation tankshown in FIG. 8 along a divide of the first chamber;

FIG. 10 is an isometric cross sectional view of the gas flotation tankshown in FIG. 8 along the dividing wall between the first and the secondchamber;

FIG. 11 is an isometric cross sectional view of the gas flotation tankshown in FIG. 8 along a divide of the second chamber;

FIG. 12 is an isometric cross sectional view of the gas flotation tankshown in FIG. 8 along a divide of the third chamber;

FIG. 13 is an isometric cross sectional view of the gas flotation tankshown in FIG. 8 along a divide of the fifth chamber; and

FIG. 14 is a schematic showing one embodiment of an interconnectingpassage including an optional coalescing media.

DETAILED DESCRIPTION

Described herein are systems, apparatuses, techniques and embodiments ofgas flotation tanks suitable for at least partially removing orcapturing contaminants or unwanted phases from a fluid, such as producedwater and methods of doing same. It will be appreciated that themethods, systems, apparatuses, techniques and embodiments describedherein are for illustrative purposes intended for those skilled in theart and are not meant to be limiting in any way. All reference toembodiments and examples throughout this disclosure should be considereda reference to an illustrative and non-limiting embodiment or anillustrative and non-limiting example.

It will be appreciated that reference to a contaminant or unwanted phaseincludes hydrocarbon or contaminants or phases that at least partiallycomprise hydrocarbon but are not limited to hydrocarbon and may includeother or alternate contaminants that behave in such a manner that a gasflotation tank could be useful in their removal from a fluid.

FIGS. 1 and 3 are isometric views of an embodiment of a flotation tank,such as a gas flotation tank, for removing contaminants, such asunwanted phases, lighter than water hydrocarbon, and/or oil, crude orrefined oil, or emulsions, from a fluid, such as produced water. A gasflotation tank is shown generally at 10 and is comprised of a tank floor50 defining the bottom of the tank 10 and a pending tank wall 45defining the periphery of the tank 10. The gas flotation tank 10 isdivided into a plurality of sequential chambers for holding andimparting a generally rotational, tumbling or circular current of theproduced water in each individual chamber in a generally longitudinaldirection of the chamber such that the surface of the fluid movestowards a skim oil trough 15 for capturing contaminant such ashydrocarbon or oil, from the surface of the fluid skimmed off the top ofthe fluid.

A series of dividing walls 65 are used to define each chamber. Althoughthe tank 10 shown throughout the figures contains five chambers, it willbe appreciated that the tank may have fewer or additional chambersdepending on the properties and rheology of produced water to becleaned, the velocity of the fluid, the rate of purification, etc. Eachchamber of the tank is connected to the adjacent chamber via aninterconnecting passage 75 (shown in FIGS. 9, 10 and 14) that allows fortransfer of the fluid from one chamber to the next.

An inlet 20, generally positioned towards an upper region of the wall 45is used to input contaminant containing fluid, such as produced water,into the tank 10 and into the first chamber of the tank 10. A slopedweir 40 bisects each of the chambers of the tank 10 for inducing therotational, tumbling or circular current in each individual chamber. Thefluid, such as produced water, is input into the first chamber from theinlet 20 in sufficient proximity to the sloped weir 40 to induce arotational, tumbling or circular current within the first chamber. Itwill be appreciated that a rotational current in the longitudinaldirection of the chamber is induced by the sloped weir 40 that promotesthe contaminant, such as lighter than water hydrocarbon, to rise to thesurface of the water in the first chamber while the cleaner and thusheavier water is pushed downwards towards the floor 50 of the tank. Askimming weir 35 separates the chambers of the tank 10 from a skim oiltrough 15 wherein contaminant, such as oil, is collected as it isskimmed over the weir from each of the chambers. In one embodiment, theskimming weir 35 comprises a one or a plurality of V-shaped notches (notshown) in the upper end of the weir 35 to allow for oil to skim over theweir and into the skim oil trough 15. In an alternative embodiment, theupper end of the skimming weir may include other shapes of notch topromote skimming of the unwanted phase into the skim oil trough 15 ormay simply contain no notches on the upper end of the skimming weir.Once skimmed from the produced water, the oil may be collected using anysuitable means.

To allow for more effective removal of contaminant via the skimming weir35 into the skim oil trough 15, before the fluid is transferred to theadjacent chamber, the interconnecting passage 75 may collect fluid fromsubstantially the base or a lower region of the sloped weir of a firstchamber thereby allowing for increased flow path of the rotating fluid.The interconnecting passage 75 may then output the fluid into theadjacent chamber on a backside of the sloped weir 40 of the adjacentchamber. The input fluid into the adjacent chamber has a rotationalcurrent imparted thereon by the sloped weir and the fluid transfer ontothe next adjacent chamber may be carried out in a similar manner. Theinterconnecting passage 75 may be formed with the slope weir 45 incombination with a baffle. Further optional features for promotingabsorption or coalescing of the contaminants as they pass through theinterconnecting passage 75 will be discussed in further detail belowwith reference to FIG. 14.

The first and the adjacent chamber, referred to as chamber two or thesecond chamber, may also be fluidly connected via a connecting port 60situated in the lower region of their dividing wall 65. By positioningthe connecting port 60 in the lower region of the dividing wall, cleanerwater is transferred from the first chamber to the second chamberallowing for equalization of the fluid levels in these adjacentchambers. It will be appreciated that the cleaner water is water havinga lower contaminant content than that input into the first chamber.

Once in the second chamber, a rotational current is again induced by asloped weir 40 to promote the contaminant to rise to the surface of thefluid in the second chamber while the cleaner water is pushed downwardstowards the floor 50 of the tank. Again, contaminant is skimmed from thesecond chamber into the skim oil trough 15 over the skimming weir 35 andthe fluid in the second chamber is further purified relative the fluidin the first chamber.

It will be noted that there is no connecting port between the second andthird chambers in order to avoid short circuiting of the fluid from thefirst chamber to the third chamber without a significant reduction incontaminant content. Avoiding short circuiting of the fluid through thetank increases the retention time in the tank and therefore generallyallows for a greater reduction in contaminant via skimming from the topof the fluid in each chamber over the skimming weir 35 and into the skimoil trough 15.

By positioning the interconnecting passage 75 a suitable distance fromthe connecting port 60 the fluid must pass through sufficient rotationalcurrent to promote the rising of the contaminant to the surface beforefluid is communicated from the second to the adjacent third chamberthereby providing fluid having a lower contaminant content to theadjacent third chamber while mitigating short circuiting.

To allow for equalization or substantial equalization of the fluidlevels between chambers wherein there is no connecting port, a fluidpassage 70 is used to allow fluid to pass through the sloped weir 40 inthe these chambers such as chamber 3. In this way, fluid is bothtransferred in the rotational current of the third chamber but can flowthrough fluid passage 70 in the event that difference in fluid levelsbetween the second and third chamber is substantially different. Ascontaminant rises to the top of the chamber it is skimmed off the topand over the skimming weir 35 and into the skim oil trough 15 therebyreducing the contaminant content in the third chamber relative thesecond chamber.

It is the combination of a connecting port between the first and secondchambers together with the interconnecting passage and the fluid passagethat allows for both fluid transfer from chamber to adjacent chamberwhile mitigating short circuiting. This setup also allows forequalization or substantial equalization of the fluid level in adjacentchambers reducing the risk of collapse of a divider wall. Once thisalternating setup of connecting ports and fluid passages is established,any suitable number of chambers may be used in the flotation tank 10.

In one embodiment, as shown throughout the figures, the fluid passage 70may be in the form of a perforated plate.

Furthermore, it will be appreciated that the sloped weir 40 may bepositioned at various points in the chambers and it is not essentialthat the sloped weirs 40 be arranged in a line as shown in the FIGS. 1to 6. For example, the sloped weirs 40 may be offset from one another asshown for example in the non-limited embodiments illustrated in FIGS. 8to 13. By adjusting the positioning of the sloped weirs 40 the rate ofthe current in each chamber may be controlled and adapted as desired oras necessary.

The sloped weirs induce a rotational current within each chamber. Therotational current allows for a lengthened flow path throughout a tankrelative a typical tank of the same diameter. The lengthened flow pathallows for the separation of phases have a specific gravity (SG)approaching that of water such as emulsified oils and viscous fluidssuch as those used in AEOR polymer flooding. In addition, the increasein flow path allows for a greater opportunity for bubbles ormicro-bubbles to come into contact substantially attach withcontaminants in the fluid thereby gradually floating or bringing them tothe surface for eventual skimming into the oil trough 15.

A manifold 25 in fluid communication with the chambers of the tank 10may be used to fill or empty the tank 10 prior to operation or formaintenance of the tank 10 as needed.

The outlet 55 may be positioned in the final chamber of the tank 10opposite the inlet chamber thereby allowing for the passage of the fluidthrough all of the chambers thus enabling the skimming of thecontaminant in each chamber resulting in the greatest reduction ofcontaminant from the fluid being output from the tank.

FIGS. 2, 3, 4, 5 and 6 shows various views of the tank 10 and the fluidpassages 70 and alternating connecting ports 60 allowing for fluidcommunication between adjacent chambers while mitigating shortcircuiting and allowing for at least partial equalization. As can beseen from the figures, an interconnecting pipe has been omitted from thetank 10. Such omission also allows for the omission of associated bypasslines and valves thereby reducing the complexity of the design andassociated costs and maintenance. Further, scalability of the design isfacilitated.

The designs described herein allow for better handling of upsetconditions as the flow from chamber to chamber is less restrictedthrough the use of the interconnecting passage 75, connecting ports 60as well as the fluid passage 70 and 85, respectively, which alternatebetween each chamber to avoid short circuiting while helping balance thefluid levels of the chambers while promoting contaminant removal throughthe avoidance of short circuiting.

The avoidance of the interconnecting pipe allows for the increasedability to build tanks capable of larger flows as the design offers alarger scalability. In addition, applications that require similar flowsbut longer retention times are also made possible.

In addition, situating the fluid passages 70 and/or 85 in the slopedweirs to create the interconnection between various chambers as well asthe interconnecting passages 75 may also act to reinforce the tank,whereas an interconnecting pipe offers little to no structural benefitand also requires its own structural supporting incremental to what wasrequired by the tank itself.

In addition to the benefits associated to operation of the tank 10, thetank 10 including the alternating setup of connecting ports 60 and fluidpassages 70 and 85 is less sensitive to tank filling and draining as theinterconnecting ports and fluid passages allow for less restricted flowfrom chamber to chamber. Alternating between fluid passages andconnecting ports helps balance the fluid levels in adjacent chambersduring filling and draining. As the fluid levels of adjacent chambers issubstantially equalized, a reduction in structural requirements isobserved relative to flotation tanks based on an interconnecting pipesetup.

It will be appreciated that the connector ports 60 and the fluidpassages 70 and 85 should alternate from chamber to chamber to ensurethat short circuiting is reduced or prevented while still allowing forat least partial equalization of the fluid level between adjacentchambers.

Further, reduced external piping and valves is required. Typicallyseveral external pipes are used for balancing during filling anddraining in a setup that includes an interconnecting pipe. These are notrequired with the tank disclosed herein.

By utilizing the alternating setup outlined herein, a longer flow pathis established that allows for removal of contaminant from the fluidinput before reaching the outlet 55 in the final chamber. In addition, asignificant component of the flow path is horizontal as opposed tovertical in typical designs. This horizontal flow path allows forbubbles or micro-bubbles to attach with contaminants to promote theirrise to the surface of the rotational fluid for skimming off.

FIG. 7 demonstrates the relationship that exists that shows thatperformance is a function of RT vs the number of sequential chambers(separators). Although the tank described herein comprised of fivechambers, this suggests that additional chambers should experience anincrease in performance.

It will be appreciated that in addition to the rotational currentinduced by the sloped weirs 40, bubbles, optionally in the form ofmicro-bubbles, may be added to each chamber via an inlet (not shown) tofurther promote the rising of the contaminant, such as hydrocarbon, tothe surface for skimming off into the skim oil trough 15. Themicro-bubbles may be added toward to base of the dividing wall,optionally in proximity to the connecting ports and act to adhere to thecontaminant, such as oil, to promote the rising of the oil to thesurface. A smaller bubble may be used to lower the rise velocity therebyincreasing the opportunity for adherence to the contaminant.Micro-bubbles may alternatively or additionally be added at the base ofthe sloped weir 40.

In addition to using the interconnecting passage 75 to allow fortransfer of fluid from one chamber to an adjacent chamber, theinterconnecting passage 75, in an alternative embodiment, may be used totransfer the liquid and also to concentrate the zone of gas/liquidcontact of the contaminant to the bubbles or micro-bubbles. For example,the bubbles or micro-bubbles may be introduced in the interconnectingpassage 75 instead of or in addition to introducing the bubbles ormicro-bubbles in the chambers themselves. Such a setup of introducingthe bubbles or micro-bubbles in a narrow zone allows for an improvedprobability of contact and attachment with the contaminant in the fluid.The introduction of gas may be concentrated to a more confined space,such as the interconnecting passage 75, and then released near thesurface as it exits the interconnecting passage 75 where it caneffectively be removed from the fluid. Typically, other technologieswork on a principle of dispersing gas in a larger volume, for examplewithin a chamber, as opposed to concentrating the gas into a narrowzone.

FIG. 14 shows an optional embodiment of an interconnecting passage thatincludes a coalescing media 100 for absorbing or coalescing contaminantsas they pass through the interconnecting passage 75. The media 100 issuspended above the opening of the interconnecting passage 75, as shownin FIG. 14, thereby allowing the fluid to pass through the media 100 asit moves to the adjacent chamber.

It will be appreciated that the media 100 may be positioned at anysuitable position within or proximate the interconnecting passage 75within or partially within the path of flow of the fluid so that fluidpasses through the media 100. It will also be appreciated that thecoalescing media 100 may be positioned in or proximate one or more oreach of the interconnecting passages 75.

The media 100 may be either a non-fixed media or a fixed media. Someexamples of non-fixed media includes “random packing” media, nutshells,etc. Some examples of fixed media includes a corrugated plate, fixedpacking, etc.

The purpose of the media 100 is to increase the droplet or particle sizeof the contaminant as it passes through the interconnecting passage 75to improve the buoyancy or floatability of the increased size of dropletor particle thereby promoting the droplet or particle to the surface forskimming.

The media 100 may be used in conjunction with the gasbubbles/microbubbles, or in place of the gas bubbles. In addition, theflow rate of the gas bubbles may be increased intermittently, asrequired or desired, to flush out and clean the coalescing media 100. Itwill be appreciated that the gas flotation tank shown in FIGS. 8 to 13operates in a similar manner to that described above with reference toFIGS. 1 to 6 with the difference that the sloped weirs 40 are offsetfrom one another in the sequential chambers. As will be appreciated, bymanipulating both the positioning of the sloped weirs and the slope ofthe weirs, the velocity profiles of the fluid may be altered to obtain amore desirable separation and/or removal of the unwanted phase orcontaminant.

It will be appreciated that the present design utilizes aninterconnecting passage to transfer the fluid from chamber to chamberand, generally, only use the fluid passages and connecting ports tobalance the chambers, whereas a serpentine tank uses perforated platesor openings to transfer fluid from one chamber to the next. Further, thepresent design may use the interconnecting channels, typically comprisedof baffles and weir plates, to create the rotational or circular flowpattern in each individual chamber. This is used to hydraulically skimthe undesired contaminants and to bring them to the surface faster andgiving them more opportunity to reach the surface more often (a resultof the water weir plates and the circular pattern they induce). As thelength of the flow path is considered to have an impact on theseparation of contaminants including phases, separation may be achievethrough the rotational or circular pattern in a smaller volume asopposed to using the length of the chamber (reusing a smaller volumeseveral times in the circular pattern instead of flowing horizontallyonce through that volume). The result of these can be a reduction ofrequired retention time which in turn dictates the volume (size) of thetank. In various embodiments, the tank as disclosed requiring ⅙th to1/12th the time (or volume) for identical scenarios. The present designallows for a single (shared) skimming means represented by the skimmingweir in combination with the skim oil trough, and a single point on thetank (nozzles, piping, and valves reduced) in which the unwantedcontaminants may be removed.

It will be appreciated that the embodiments outlined herein are notintended to be limiting in any way and are merely illustrative of theinvention. Modifications, alternations, substitutions and extensions ofthe design may be made which should be considered to be within the scopeand spirit of the invention.

We claim:
 1. A flotation tank for removing a contaminant from fluidinput into the flotation tank, the flotation tank comprising; a floordefining a bottom of the tank and a depending wall defining the sides ofthe tank; a series of adjacent chambers within the tank separated fromeach other by dividing walls, each chamber comprising a sloped weir forinducing a rotational current within the chamber; a skim oil troughspanning each chamber and separated from each chamber by a skimmingweir, the skimming weir opposite the sloped weir; an inlet in fluidcommunication with a chamber of the series of adjacent chambers forinputting a fluid comprising a contaminant, the inlet situated proximatethe sloped weir of the series of adjacent chambers for inducing arotational current to fluid input into the chamber; each chamber influid communication with the adjacent chambers via an interconnectingpassage positioned substantially towards the bottom of the dividing wallof each chamber and substantially opposite the skim oil trough, theinterconnecting passage allowing passage of fluid from a chamber to abackside of the sloped weir of the adjacent chamber; a connector port inthe dividing wall between two adjacent chambers for providing fluidcommunication between the two adjacent chambers; a fluid passage in thesloped weir of at least one of the chambers of the series of adjacentchambers allowing for fluid transfer between adjacent chambers throughthe sloped weir of the at least one chamber; and an outlet in fluidcommunication with one of the chambers of the series of adjacentchambers outputting produced water; a coalescing media positioned in orproximate one or more of the interconnecting passages for absorbing orcoalescing contaminants as they pass through the interconnectingpassage; wherein the connector port and the fluid passage are situatedin alternating adjacent chambers.
 2. The flotation tank of claim 1,wherein the connector port is positioned in the base of the dividingwall proximate the skimming weir.
 3. The flotation tank of claim 1,wherein the interconnecting passage is positioned at one end proximatethe base of the sloped weir and at the other end in proximity to abackside of the sloped weir of the adjacent chamber.
 4. The flotationtank of claim 1, wherein the fluid passage is positioned proximate thebase of the sloped weir.
 5. The gas flotation tank of claim 1, whereinthe fluid passage is a perforated plate in the sloped weir.
 6. Theflotation tank of claim 1, wherein the outlet is positioned proximatethe base of the wall of the final chamber.
 7. The flotation tank ofclaim 1, wherein the inlet is positioned in the first chamber.
 8. Theflotation tank of claim 1, wherein each set of adjacent chamberscomprises either a connector port or a fluid passage in alternatingformat allowing for equalization of the fluid level in adjacent chamberswhile preventing short circuiting of the fluid through the tank to thefinal chamber.
 9. The flotation tank of claim 6, further comprising amanifold in fluid communication with each chamber for inputting orwithdrawing fluid from the tank.
 10. The flotation tank of claim 1,wherein the sloped weirs of the tank are aligned with one another in theadjacent chambers.
 11. The flotation tank of claim 1, wherein the slopedweirs of the tank are offset with one another in at least two of theadjacent chambers.
 12. The flotation tank of claim 1, wherein an upperedge of the skimming weir comprises at least one notch to promotetransfer of the unwanted phase into the skim oil trough.
 13. Theflotation tank of claim 1, further comprising an inlet in fluidcommunication with each chamber for injecting a gas into the chamber,optionally in the form of micro-bubbles.
 14. The flotation tank of claim1, wherein the contaminant comprises hydrocarbon, emulsified oils, orheavy oils.
 15. The flotation tank of claim 1, wherein the fluid isproduced water.
 16. The flotation tank of claim 1, wherein thecoalescing media is a fixed media.
 17. The flotation tank of claim 1,wherein the coalescing media is a non-fixed media.
 18. The flotationtank of claim 1, wherein the coalescing media is positioned in theinterconnecting passage.